Decca CTV25 EHT tower Versions.

Didn't stock the Decca sets so cannot comment, we stocked the Bush though.

No experience of these either but the Mazda book of Pal Receiver Servicing mentions the CTV25 and CTV25CE. The latter does away with the potentially troublesome (my words, not theirs) 25Kv LOPT with GY and PD combination and replaces them with usual 8Kv overwind and tripler. The picture of the CTV25CE chassis appears to be similar to the one fitted in your CTV22C.

John.

Hi John,

yes I have that version of the chassis in my 22" Decca CTV22C the same chassis as you say appeared in the later CTC25 (see below). I'm wondering if my Decca CTV25 has the MK1 tower or later MK2

Picture from my Decca CTV25 workshop manual MK3

I suspect that may be the MK3 above, I wonder if the MK2 was a 25Kv LOPT with some sort of flame retardant properties or a Davy lamp modification as with the Bush CTV25. I have no idea if the MK1s suffered the same issues as the burning Bushes but from the comment over on UKVRR I suspect that maybe the case.

John.

Judging by what you posted in your link above: https://www.radios-tv.co.uk/1967-decca-ctv25/

It looks as though your set has the early version, or at least an earlier version as the dire X-ray warnings the PD500 shunt stabiliser and GY501 EHT rectifier would not be needed with the tripler version.

Plus the size of the "smoke stack" looks to be consistent with that assumption compared to the size of the Lop section pictured in the manual for the Tripler version.

Edit: Hi John, I was wondering exactly this:

 I wonder if the MK2 was a 25Kv LOPT with some sort of flame retardant properties or a Davy lamp modification as with the Bush CTV25. I have no idea if the MK1s suffered the same issues as the burning Bushes but from the comment over on UKVRR I suspect that maybe the case.

However I don't really know and so refrained from posting, also hence my wording "of at least an earlier version"

Red_to_Black said
Judging by what you posted in your link above: https://www.radios-tv.co.uk/1967-decca-ctv25/

It looks as though your set has the early version, or at least an earlier version as the dire X-ray warnings the PD500 shunt stabiliser and GY501 EHT rectifier would not be needed with the tripler version.

Plus the size of the "smoke stack" looks to be consistent with that assumption compared to the size of the Lop section pictured in the manual for the Tripler version.

Hi Baz,

You've misunderstood my post, I know I'm dense but not that dense

I'm fully aware my CTV25 does not employ a tripler inside the stack. I know it is the full valved EHT generation it also has a NOS LOPT fitted. That wasn't my query, my question was in relation to the type of physical tower employed to contain it all.

Ah Right,

I put that down to it being Friday night 

Then I think John also answered about the MK3 version being much smaller as pictured on the page of the manual, as I sort of did the other way around. 

Plus the size of the "smoke stack" looks to be consistent with that assumption compared to the size of the Lop section pictured in the manual for the Tripler version.

Unless I am still being a bit dense and still misunderstanding ? not be the first time lol

Red_to_Black Said

Ah Right,

I put that down to it being Friday night 

All is forgiven

Yes so my Decca CTV25 has either a MK1 tower or a MK2 tower and my CTV22C is the MK3 version. I see John has asked Glyn for more clarification on the MK1/2 so hopefully he may be able to confirm. He might even be surprised to see my one still working.

I would be interested to know too, I had similar thoughts to John, but didn't know for sure RE: the MK2 version.

Will wait and see what Glyn replies back with.

I have what I think is a Mkl smoke stack service manual but I'm not sure. I'll copy a bit when I get up - it's a fancy book in colour with plenty of detail in waveforms and PCB tracking. Marybe it can clear up some of the doubt. 

Here's a scan of the front Cover (it does cover the tall, 25kV overwind version) :

Well I've dug my Decca workshop manual out and did a bit more thorough reading. The Manual is no small affair and very comprehensive, it covers the CTV19, CTV22 and CTV25. I also have within that manual there is issue 4 of the one you show above.

I can therefore now confirm that the tripler version of this chassis was known as the MK.2 and the tower version as MK.1. Therefore my Decca CTV25 is a working example of the MK.1, probably not that many about.

Whats absolutely superb about this manual and what I've not seen before on any other, is on the plan view diagrams it shows signal paths. For example colour coded lines show where the audio, video and sync paths route on the luminance module and through what components, all very good for aiding fault diagnosis.

This manual will be a superb help when I get around to rebuilding the CTV22 with all its snipped wires and missing connections.

I was waiting for JC to reply first

It does not look like Glyn (Welsh Anorak) came up with much definitively , so what is the consensus ? is there a Mk2 and Mk3 ? or just a MK1 and 2 ?

More to the point did the later tripler version still use the shunt stabiliser ? I do understand that the mists of time do degrade ones memory , I for one these days am extremely rusty with remembering stuff that was second nature not that long back.

It is really strange that I can recall some faults getting on for thirty years ago now, but then often forget about fairly in depth stuff I wrote only a few short years ago, I recall Rich (SB) of this parish saying much the same thing a few years ago about a fault report he wrote in the TV mag previously.

early on set of dementia ? , or just our heads filled with more technical crap that we need on a day to day basis

I really don't know, but Mike Phelans phrase of  his wonderful "forgettory" is becoming a lot more prevalent for me these days , unless it is just because with being out of the trade now we are becoming "ring rusty", that or old age is creeping up lol boo! hiss!

Red_to_Black said

More to the point did the later tripler version still use the shunt stabiliser ?

No the MK2. (tripler version) did not use a  *shunt stabiliser.

Inside the cage: PL, PY and tripler

* Interestingly the year before in 1967, the Baird M702W used a tripler and still employed a PD500 EHT shunt stabiliser. By 1968 they too had removed the PD500 with EHT stabilisation provided by a VDR on the M718

So I take it there is only a Mk 1 and 2 then ?, Glyn was a bit vague, I wonder if he is mixing up chassis/versions ?

It does happen with the mists of time , I myself have been known to get it mixed up before now , this/these chassis certainly pre-dates my time in the trade, although I do recall seeing one or two in my very early years in the trade, but I have had effectively zero experience of any of them.

Chris said

* Interestingly the year before in 1967, the Baird M702W used a tripler and still employed a PD500 EHT shunt stabiliser. By 1968 they too had removed the PD500 with EHT stabilisation provided by a VDR on the M718  

The Wireless World color receiver also used a tripler plus PD500 shunt stabilliser, accompanied by many warnings about the danger from X-rays.

As it is unlikely that I myself would be in possession of a CTV25 in any guise, it would be great to see some pictures inside the magic big black box one day.......

(Sorry for using one of your pictures Chris , just couldn't find a better one).

I'll take one of inside the Decca later today. But quick to hand if you want to see what's inside the G6's Black box, its truly terrifying to behold.

Here we go...........you have been warned, Lead-lined gussets at the ready?

G6 Black-Box

Cover removed

Close up of the fiendish device. Mur!-Hurrr!-Hurrrrrr! ( cue thunder crack)

PD500 Shunt stabiliser at the top, GY501 EHT rectifier in the middle pluged into the top of teh 25kV overwind

The bottles that sit within

I didn't work on any G6's but the LOPTX looks very similar to the Pye/Ekco dual standard CTV TX.

The over wind and valve mounting look identical. Similar construction for the rest of the TX. 

Not sure why but the high voltage circuits never worried me, just knew they required treating with respect. So I never thought of them as fiendish.